Utilization of spraying apparatus in the application of a coating material such as a paint composition or other liquid is well recognized in the art as an efficient way to provide uniform deposition of the coating material on a workpiece. Various types of spraying apparatus have been devised to accomplish this deposition, and include conventional spray guns, spray guns having electrostatic charging means, and spray guns provided with gas shroud means along with electrostatic charging means whereby gas concentrically envelops an electrically charged spray stream as the stream travels from the spray gun to a workpiece to be coated. An example of spraying apparatus which embodies electrostatic charging means and gas shroud means is found in U.S. Pat. No. 4,106,697 to Sickles et al.
When a gas-shrouded induction charging spray apparatus is employed, an electrically charged spray of liquid particles travels to the workpiece and is atmosphere-protected from the ambient atmosphere by the gas enveloping the spray, thereby permitting controlled humidity, temperature, and appropriately-conditioned gaseous requirements. However, because the liquid particles comprising the spray are charged, they have a tendency to drift to any site of lower electrical potential, including the housing itself which provides origination of the gas shroud envelope. As a result, prolonged periods of spraying can result in coating material build-up on this housing. Further, because substantially all of the charged liquid particles of the spray have the same polarity, they repel each other and can therefore broaden the spray stream beyond a desired configuration.
It is therefore an object of this invention to enhance the axial integrity of the spray stream upon its exiting from the spraying apparatus in travel toward a workpiece to be coated. It is a further object of the invention to inhibit deposition of charged sprayed liquid particles on the spraying apparatus and its fixtures, and to simultaneously, via a repulsion effect, drive charged particles toward the workpiece and thereby improve coating deposition efficiency. These and other objects will be apparent throughout the body of this application.